1. Field of the Invention
The present invention generally relates to the field of methods for producing magnetic material based on a substance system comprising a rare-earth element, iron, nitrogen and carbon, and optionally hydrogen. More particularly, the present invention relates to the field of methods for processing high Tc Smxe2x80x94Fexe2x80x94N and Smxe2x80x94Fexe2x80x94C, N magnetic materials. In particular, the present invention relates to the field of methods for synthesis of magnetic materials by polymerizing, pyrolyzing and sintering amide precursor in an inert or reduced atmosphere.
2. Description of the Prior Art
Ferromagnetic materials and permanent magnets are important materials widely used in electrical and electronic products. The well-established Nd2Fe14B based magnets have a high saturation magnetization, moMS of 1.6 T, high anisotropy field, moHA of 6.7 T and high energy product, (BH)max, of 360 kJ/m3 at room temperature. However, the low Curie temperature, Tc, of 310xc2x0 C. seriously reduces the performance above room temperature.
In recent years, many studies have been conducted on the nitrides and carbides of rare earth iron compounds, and two compounds, Sm2Fe17N2.3 and Sm2Fe17C2, have been formed with characteristics superior to Nd2Fe14B. For example, the parameters for Sm2Fe17N2.3 are Tc=485xc2x0 C., moMs=1.5 T, moHA=15 T and for Sm2Fe17C2 are Tc=407xc2x0 C., moMs=1.4 T, moHA=13.9 T. These parameters imply that magnets made from these alloys could have an energy product as high as 470 kJ/m3, with a superior Tc.
However, the a-Fe precipitated during the nitridation of Smxe2x80x94Fe alloy is found to reduce the performance of hard magnets. Furthermore, stability of Smxe2x80x94Fexe2x80x94N hard magnetic materials is limited at temperature above 300xc2x0 C. A significant enhancement of coercivity of Smxe2x80x94Fexe2x80x94N is observed with a refinement of the material""s microstructure, including homogeneity both in composition and grain size distribution, as well as second phase effect.
The state-of-the-art of the process for rare earth iron nitride, or rare earth iron carbide, or rare earth iron hydride is to form rare earth iron alloy first followed by nitridation, carbonation and hydridation. The lattice constants increase about 6% percent after nitridation from Sm2Fe17 to Sm2Fe17N2+xcex4.
One way to fabrication of nitride materials is to use metal amides and derivatives. High purity and homogeneous nitride and carbonitride materials, such as aluminum nitride, titanium nitride, molybdenum carbonitride, have been synthesized by decomposition of polymerized amide precursors, such as (R2N)3Al, R(H)AlN(H)R, Ti(NR2)n, where R stands for alkyl groups.
The following seven (7) prior art references are found to be pertinent to the field of the present invention:
1. U.S. Pat. No. 5,137,587 issued to Schultz et al. on Aug. 11, 1992 for xe2x80x9cProcess For The Production Of Shaped Body From An Anisotropic Magnetic Material Based On The SMxe2x80x94FExe2x80x94N Systemxe2x80x9d (hereafter the xe2x80x9cSchultz Patentxe2x80x9d);
2. U.S. Pat. No. 5,137,588 issued to Wecker et al. on Aug. 11, 1992 for xe2x80x9cProcess For The Production Of An Anisotropic Magnetic Material Based Upon The SMxe2x80x94FExe2x80x94N Systemxe2x80x9d (hereafter the xe2x80x9cWecker Patentxe2x80x9d);
3. U.S. Pat. No. 5,288,339 issued to Schnitzke et al. on Feb. 22, 1994 for xe2x80x9cProcess For The Production Of Magnetic Material Based On The SMxe2x80x94FExe2x80x94N Systemxe2x80x9d (hereafter the xe2x80x9cSchnitzke Patentxe2x80x9d);
4. U.S. Pat. No. 5,665,177 issued to Fukuno et al. on Sep. 9, 1997 for xe2x80x9cMethod For Preparing Permanent Magnet Material, Chill Roll, Permanent Magnet Material, And Permanent Magnet Material Powderxe2x80x9d (hereafter the xe2x80x9cFukuno Patentxe2x80x9d);
5. U.S. Pat. No. 5,720,828 issued to Strom-Olsen on Feb. 24, 1998 for xe2x80x9cPermanent Magnet Material Containing A Rare-Earth Element, Iron, Nitrogen And Carbonxe2x80x9d (hereafter the xe2x80x9cStrom-Olsen Patentxe2x80x9d);
6. U.S. Pat. No. 5,788,782 issued to Kaneko et al. on Aug. 4, 1998 for xe2x80x9cRxe2x80x94FExe2x80x94B Permanent Magnet Materials And Process Of Producing The Samexe2x80x9d (hereafter the xe2x80x9cKaneko Patentxe2x80x9d); and
7. Journal Of Organometallic Chemistry 87 (1975) 301-309 (hereafter the xe2x80x9cJournalxe2x80x9d).
The Schultz Patent discloses a process for the production of shaped body from an anisotropic magnetic material based on the Smxe2x80x94Fexe2x80x94N system. The system includes a crystalline, hard magnetic phase with a Th2Zn17 crystal structure, wherein N atoms are incorporated in the crystal lattice, is produced by compacting a powder Smxe2x80x94Fe preliminary product with a Smxe2x80x94Fe phase having a magnetically isotropic structure, followed by hot-shaping to provide an intermediate product with a Smxe2x80x94Fe phase having a magnetically anisotropic structure, followed by heat treating the intermediate product in a nitrogen atmosphere to provide a Smxe2x80x94Fexe2x80x94N hard magnetic phase.
The Wecker Patent discloses a process for the production of an anisotropic magnetic material based upon the Smxe2x80x94Fexe2x80x94N system. The magnetic material of the Smxe2x80x94Fexe2x80x94N system includes a crystalline, hard magnetic phase with a Th2Zn17 crystal structure, wherein N atoms are incorporated in the crystal lattice, is produced. First a preliminary product is formed by sintering a Smxe2x80x94Fe powder which is oriented in a magnetic field to provide a sintered body having a two-component Smxe2x80x94Fe phase. The sintered body is heat treated in a nitrogen atmosphere to form the Smxe2x80x94Fexe2x80x94N hard magnetic phase.
The Schnitzke Patent discloses a process for the production of magnetic material based on the Smxe2x80x94Fexe2x80x94N system of elements. The magnetic material of the Smxe2x80x94Fexe2x80x94N system exhibits a crystalline hard magnetic phase with a Th2Zn17 crystal structure, wherein N atoms are incorporated in the crystal lattice. A preliminary product has a dual component Sm2Fe17 phase is produced by mechanical alloying followed by thermal treatment to achieve the desired microstructure. The preliminary product may also be obtained by a rapid-quenching technique.
The Fukuno Patent discloses a method for preparing permanent magnet material, chill roll, permanent magnet material, and permanent magnet material powder. A permanent magnet material is prepared by cooling with a chill roll a molten alloy containing R wherein R is at least one rare earth element inclusive of Y, Fe or Fe and Co, and B. The chill roll has a plurality of circumferentially extending grooves in a circumferential surface, the distance between two adjacent ones of the grooves at least in a region with which the molten alloy comes in contact being 100 to 300 xcexcm average in an arbitrary cross section containing a roll axis. Permanent magnet material of stable performance is obtained since the variation of cooling rate caused by a change in the circumferential speed of the chill roll is small. The variation of cooling rate is small even when it is desired to change the thickness of the magnet by altering the circumferential speed. The equalized groove pitch results in a minimized variation in crystal grain diameter.
The Strom-Olsen Patent discloses a permanent magnet material containing a rare-earth element, iron, nitrogen and carbon. They are produced by gas absorbing nitrogen and carbon sequentially into a parent intermetallic compound. The resulting magnetic materials have high TC, xcexcoMs and xcexcoHA, are essentially free of xcex1-Fe, and have a coercivity at 300xc2x0 K. of at least 1.5 T. Anisotropic magnetic materials are produced by pretreating the intermetallic compound, which contains carbon, by powder sintering or oriented hot shaping, followed by nitriding and/or carbiding.
The Kaneko Patent discloses Rxe2x80x94Fexe2x80x94B permanent magnet materials having a good oxidation resistance and magnetic characteristics, and process of producing the same capable of pulverizing efficiently, whereby an Rxe2x80x94Fexe2x80x94B molten alloy having a specific composition is cast into a cast piece having a specific plate thickness and a structure, in which an R-rich phase is finely separated below 5 xcexcm, by a strip casting process.
The Journal discloses a Ti(xe2x80x94NMexe2x80x94SiMe2xe2x80x94SiMe2xe2x80x94MeNxe2x80x94)2 (I) has been obtained from the reaction of LiNMeSiMe2NMeLi with TiBr4. It forms yellow crystals of considerable stability which can be sublimed without decomposition. Its 1H NMR, IR and Raman spectra are reported. The crystal structure of I was determined by X-ray diffraction and was refined to R=0.059. The titanium atom in the spiro type molecule is tetrahedrally coordinated by nitrogen atoms with TiN distances of 1.905 xc3x85 SiN and SiSi distances in the slightly puckered five-membered rings are 1.733 and 2.355 xc3x85, respectively.
It is desirable to provide a method for the production of magnetic material based on a substance system comprising a rare-earth element, iron, nitrogen and carbon. It is also desirable to provide a method for synthesis of magnetic material from rare-earth metal and iron amide and formation of magnetic materials by polymerizing, pyrolyzing and sintering amide precursor in an inert or reduced atmosphere.
The present invention is a novel method for synthesis of intermetallic substances containing iron, a rare earth element, nitrogen and/or carbon.
It is an object of the present invention to provide a method of fabricate rare earth iron nitride and carbonitride from polymerized metal amides and derivatives.
It is also an object of the present invention to provide intermetallic substances in the form of magnetic materials, including isotropic magnetic materials and aniostropic magnetic materials.
It is an additional object of the present invention to provide a method to fabricate rare earth iron nitride and carbonitride powder.
It is a further object of the present invention to provide a method for sintered magnetic articles.
The present invention method for fabrication of rare earth iron nitride and carbonitride magnetic powder as well as shaped magnets comprises the following basic steps:
(a) Synthesis of metal amide precursors:
(i) Synthesis of metal amide precursors via electrolysis in an organic electrolyte which containing alkylamine, acetonitrile, and tetrabutylammonium bromide salt; or
(ii) Synthesis of metal amide precursors by reacting lithium dialkylamine with metal chloride, bromide or chloride-THF complex (THF=Tetrahydrofuran).
(b) Polymerization of metal alkylamides through partially aminolysis and condensation.
(c) Sintering of polymeric precursor to form magnetic materials in an inert or reduced atmosphere.
(i) Nitride and carbonitride magnetic powder. The powderized magnetic materials are formed through decomposition of polymeric precursor in an inert (nitrogen) or reduced atmosphere (ammonia).
(ii) Sintered nitride and carbonitride magnets. Fabrication of sintered nitride and carbonitride magnets is impossible via conventional process due to the limitation of the nitridation and carbonation. A novel approach to fabricate sintered rare earth iron nitride and carbonitride bulk magnet is invented. Shaped green body is formed first by pressing partially pyrolyzed polymerized powder, followed by sintering in an inert or reduced atmosphere under pressure.
Further novel features and other objects of the present invention will become apparent from the following detailed description, discussion and the appended claims, taken in conjunction with the drawings.